Download Nucleic Acids

CHAPTER 3
The Molecules of Life
PowerPoint® Lectures for
Essential Biology, Third Edition
– Neil Campbell, Jane Reece, and Eric Simon
Essential Biology with Physiology, Second Edition
– Neil Campbell, Jane Reece, and Eric Simon
Lectures by Chris C. Romero
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Biology and Society:
Does Thanksgiving Dinner Make You Sleepy?
• After finishing a huge Thanksgiving dinner,
– Many people feel especially lethargic and a few
even doze off.
• Many people think that turkey makes you sleepy.
– Is there a biological basis to this claim?
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• Turkey meat is high in tryptophan.
– Tryptophan is a molecule that is converted in your
body to serotonin, which promotes sleep.
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Figure 3.1
• However, there is little evidence
– That a turkey dinner encourages sleep more than
any other meal.
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Organic Molecules
• A cell is mostly water.
– The rest of the cell consists mostly of carbonbased molecules.
– Organic chemistry is the study of carbon
compounds.
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Carbon Chemistry
• Carbon is a versatile atom.
– It has four electrons in an outer shell that holds
eight.
– Carbon can share its electrons with other atoms to
form up to four covalent bonds.
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• Carbon can use its bonds to
– Attach to other carbons.
– Form an endless diversity of carbon skeletons.
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Figure 3.2
• The simplest organic compounds are hydrocarbons.
– These are organic molecules containing only
carbon and hydrogen atoms.
– The simplest hydrocarbon is methane.
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Figure 3.3
• Larger hydrocarbons
– Are the main molecules in the gasoline we burn in
our cars.
• The hydrocarbons of fat molecules provide energy
for our bodies.
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Figure 3.4
• Each type of organic molecule has a unique threedimensional shape that defines its function in an
organism.
– The molecules of your body recognize one
another based on their shapes.
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• The unique properties of an organic compound
depend not only on its carbon skeleton but also on
the atoms attached to the skeleton.
– These atoms are called functional groups.
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Figure 3.5
Giant Molecules from Smaller Building Blocks
• On a molecular scale, many of life’s molecules are
gigantic.
– Biologists call them macromolecules.
– Examples: DNA, carbohydrates
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• Most macromolecules are polymers.
– Polymers are made by stringing together many
smaller molecules called monomers.
– Cells link monomers by dehydration reactions.
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Figure 3.6a
• Organisms also have to break down
macromolecules.
– Cells do this by a process called hydrolysis.
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Figure 3.6b
Biological Molecules
• There are four categories of large molecules in
cells:
– Carbohydrates
– Lipids
– Proteins
– Nucleic acids
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Carbohydrates
• Carbohydrates include:
– Small sugar molecules in soft drinks
– Long starch molecules in pasta and potatoes
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Monosaccharides
• Monosaccharides are simple sugars.
– Glucose is found in sports drinks.
– Fructose is found in fruit.
• Honey contains both glucose and fructose.
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Figure 3.7
• The monosaccharides glucose and fructose are
isomers.
– They have the same formula, but their atoms are
arranged differently.
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Figure 3.8
• In aqueous solutions, monosaccharides form rings.
• Monosaccharides are the main fuel that cells use
for cellular work.
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Figure 3.9
Disaccharides
• A disaccharide is a double sugar.
– It is constructed from two monosaccharides.
• Disaccharides are joined through a dehydration
reaction.
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Figure 3.10
• Lactose is another type of disaccharide.
– Some people have trouble digesting lactose, a
condition called lactose intolerance.
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Figure 3.11
• The most common disaccharide is sucrose,
common table sugar.
– It consists of a glucose linked to a fructose.
– Sucrose is extracted from sugar cane and the roots
of sugar beets.
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• The United States is one of the world’s leading
markets for sweeteners.
– The average American consumes about 64 kg of
sugar per year.
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Figure 3.12
Polysaccharides
• Complex carbohydrates are called polysaccharides.
– They are long chains of sugar units.
– They are polymers of monosaccharides.
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Figure 3.13
• One familiar example of a polysaccharide is starch.
– Plant cells store starch for energy.
– Potatoes and grains are major sources of starch in
the human diet.
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• Animals store excess sugar in the form of a
polysaccharide called glycogen.
– Glycogen is similar in structure to starch.
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• Cellulose is the most abundant organic compound
on Earth.
– It forms cable-like fibrils in the tough walls that
enclose plants.
– It is a major component of wood.
– It is also known as dietary fiber.
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• Most animals cannot derive nutrition from fiber.
– Grazing animals survive on a diet of cellulose
because they have prokaryotes in their digestive
tracts that can break down cellulose.
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Figure 3.14
• Simple sugars and double sugars dissolve readily in
water.
– They are hydrophilic, or “water-loving.”
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Low-Carb Diets
• In recent years, “low-carb diets” have become
popular.
– But consumers need to be wary of products
boasting that they are “low-carb” because they
can sometimes be unhealthy.
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Lipids
• Lipids are hydrophobic.
– They do not mix with water.
– Examples: fats and steroids
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Fats
• Dietary fat consists largely of the molecule
triglyceride.
– Triglyceride is a combination of glycerol and
three fatty acids.
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Figure 3.15a
• Fats perform essential functions in the human
body:
– Energy storage
– Cushioning
– Insulation
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• Unsaturated fatty acids
– Have less than the maximum number of
hydrogens bonded to the carbons.
• Saturated fatty acids
– Have the maximum number of hydrogens bonded
to the carbons.
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Figure 3.15b
• Most animal fats have a high proportion of
saturated fatty acids, which can be unhealthy.
– Example: butter
• Most plant oils tend to be low in saturated fatty
acids.
– Example: corn oil
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• Not all fats are unhealthy.
– Some fats perform important functions in the
body and are essential to a healthy diet.
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Figure 3.16
Steroids
• Steroids are very different from fats in structure
and function.
– The carbon skeleton is bent to form four fused
rings.
• Cholesterol is the “base steroid” from which your
body produces other steroids.
– Example: sex hormones
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Figure 3.17
• Synthetic anabolic steroids are controversial.
– They are variants of testosterone.
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• Some athletes use anabolic steroids to build up
their muscles quickly.
– However, these substances can pose serious
health risks.
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Figure 3.18
Proteins
• A protein is a polymer constructed from amino acid
monomers.
• Proteins perform most of the tasks the body needs
to function.
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Figure 3.19
The Monomers: Amino Acids
• All proteins are constructed from a common set of
20 kinds of amino acids.
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• Each amino acid consists of
– A central carbon atom bonded to four covalent
partners.
– A side group that is variable among all 20.
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Figure 3.20
Proteins as Polymers
• Cells link amino acids together by dehydration
reactions.
– The resulting bond between them is called a
peptide bond.
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Figure 3.21
• Your body has tens of thousands of different kinds
of protein.
– The arrangement of amino acids makes each one
different.
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• Primary structure
– The specific sequence of amino acids in a protein
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Figure 3.22
• A slight change in the primary structure of a
protein affects its ability to function.
– The substitution of one amino acid for another in
hemoglobin causes sickle-cell disease.
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Figure 3.23
Protein Shape
• Proteins have four levels of structure.
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Figure 3.24
What Determines Protein Structure?
• A protein’s shape is sensitive to the surrounding
environment.
– Unfavorable temperature and pH changes can
cause a protein to unravel and lose its shape.
– This is called denaturation.
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Nucleic Acids
• Nucleic acids are information storage molecules.
– They provide the directions for building proteins.
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• There are two types of nucleic acids:
– DNA, deoxyribonucleic acid
– RNA, ribonucleic acid
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• The genetic instructions in DNA
– Must be translated from “nucleic acid language”
to “protein language.”
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Figure 3.25
• Nucleic acids are polymers of nucleotides.
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Figure 3.26
• Each DNA nucleotide has one of the following
bases:
– Adenine (A)
– Guanine (G)
– Thymine (T)
– Cytosine (C)
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Figure 3.27
• Nucleotide monomers are linked into long chains.
– These chains are called polynucleotides, or DNA
strands.
– A sugar-phosphate backbone joins them together.
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Figure 3.28a
• Two strands of DNA join together to form a double
helix.
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Figure 3.28b
• RNA, ribonucleic acid, is different from DNA.
– Its sugar has an extra OH group.
– It has the base uracil (U) instead of thymine (T).
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Figure 3.29
Evolution Connection:
DNA and Proteins as Evolutionary Tape Measures
• Evolutionary relationships between organisms can
be assessed.
– Molecular genealogy extends to relationships
between species.
– Biologists use molecular analysis of DNA and
protein sequences for testing evolutionary
hypotheses.
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Figure 3.30